Saponification of cellulose esters



Patented Jan. 31, 1933 UNITED STATES CAHILLE DBEYFUS, OF NEW YORK, N. Y.,

m WILLIAM. wmrnnmn, on eman- LAND, MARYLAND, ASSIGNORS TO CELANESE CORPORATION OF AMERICA, A. COB- I'OEATION OF IIIIIEJILA'WARIE;

SAPONIEIGATION OF CELLULOSE ESTERS 30 Drawing.

This invention relates to the treatment of products made from or contain'in esters of cellulose and is directed particu arly to an improved method of saponifying such esters of cellulose. Y

' An object of this invention is to saponify yarns, fabrics, films, and other materials containin esters of cellulose in such a manner that the valuable properties of such esters 19 will'be retained.

Another object of this invention is to provide a process for the saponification of organic cellulose ester materials whereby some of the valuable properties of the materlal willbe enhanced.

Still another object of this invention is to saponify the or anic cellulose esters under such conditions at a material of greatly increased strength is obtained.

Another object of our invention is to render yarns, films, etc., containing organic esters of cellulose capable of absorbing atmospheric humidity and becoming more suitable for working in textile operatlons.

The saponification of materials containing cellulose esters has long been proposed. The original intent of such-saponification was to render the materials containing the same amenable to dyeing with cotton dyes, as no,

suitable dyes for these esters were at that time known. Under such practice a large and uneven degree of saponification resulted with a consequent loss of weight in the materials thus treated. V

All of the saponification processes suggested to date have utilized an aqueous solution of an alkali or other material which would yield free hydroxyl ions in solution. This saponification treatment, however, was

objectionable since in addition to the great loss in weight, it resulted in the cellulose esters losing most of their distinctive and desirable properties such as stren h, elasticity, hand, appearance, etc. Also t e sapomficatiqn yielded a regenerated cellulose which Application filed June 20,

' troducing the ester or ester materials into 1928. Serial No. 287,034.

material is rather weak in tensile strength. Moreover, with the old rocess is was diflicult to control the sapon' cation so as to yield a product which was uniform in appearance and evenly saponified.

Yarns and fabrics containing organic derlvatives of cellulose have obtained a wide use in the textile field because of their many desirable properties. It has been felt, however, that its use would be greatly increased if its strength and resistance to heat could be increased. Our invention has overcome this difiiculty since it results in the saponification of the esters without deleteriously affecting the properties which render them useful for textile purposes.

We. have now found that if the saponifi'cation. of the cellulose esters is efiected by in- ,mains possessing desirable qualities not.

found in regenerated cellulose.

The cellulose ester materials treated in accordance with this process possess another marked advantage, not only over materials saponified by other known methods but also over the cellulose ester materials in their original state. This is their remarkabe increase of strength as compared with unsaponified cellulose or cellulose esters saponified by the old methods. In several instances the increases in the dry tenacity of the yarn treated in accordance with this invention 90 have been higher than 30%, even though the yarn has been saponified over 90 to 95%.

The cellulose ester material, even though it has been very largely saponified in accordance with this invention, also has its ironing temperature raised appreciably. Moreover, under proper regulation of thesaponification it is possible to obtain a product which is soluble in glacial acetic acid and does not absorb cotton dyes even though it is very highly saponified. In accordance with this invention the cellulose ester material is subjected to the action of an atmosphere of a base and water vapor at comparatively low temperatures. There should be enough of the base present to effect the desired degree of saponification.

The material to be treated can be in any desired form such as yarn or thread in hanks or on bobbins or pirns, in the form of knitted or woven fabric, garments or in the form of films, bristles, etc. The desired gaseous atmosphere can be obtained in any suitable manner for instance, by suspending the cellulose ester material in a large aspirator connected with a container having therein a 28% solution of ammonia or other volatile base.

Without desiring to be limited to such specific concentrations or particular reagents it can be stated that very good results were obtained by first extracting the cellulose ester material to remove any lubricants which might be present, drying the material at 100 C. and then subjecting the same to the action of an atmosphere saturated with ammonia and water vapor at temperatures of 25 C; to 30 C. The cellulose ester material was suspended in a large aspirator connected with a flask containng an ammonia solution. The time during which the reaction is allowed to proceed will vary depending upon the extent of saponification desired. Thus at the end of 4 hours an approximate saponification of 3% was found; at the end of 6 hours 12.5%; at the end of 8 hours 56% at the end of 24 hours 99%. The time can be shortened by utilizing a slightly higher temperature for the reaction atmosphere but the lower temperatures are preferable since they result in a more uniform saponification.

The materials which may be used to effect the saponification can be ammonium hydroxide, methyl amine, dimethyl amine or any other volatile base which will yield hydroxyl ions under the conditions of operation. The base selected, however, should be compatible with water vapor since the latter must be present in the reaction atmosphere.

As previously stated, good results were obtained utilizing an aqueous solution of ammonia of approximately 28% strength.

This process is applicable not only to yarns, threads, films, etc. made of or containmg organic esters of cellulose but also to such materials when they contain mixtures of such esters. Also it can be applied to such cellulose ester materials when they are admixed or formed with other fibres, whether the latter are animal, vegetable or artificial in nature. Thus a fabric containing" cellulose acetate in admixture with cotton, Wool, silk, linen, reconstituted cellulose (rayon) can be effectively treated in accordance with this invention. I

The fact that the cellulose remaining after complete saponification according to our invention is different from normally regenerated cellulose is further evidenced by the increase in strength or tenacity noted in the saponified yarn. This indicates that while there has been a loss of acetyl radicals in the cellulose molecules there has been only a slight loss of bonds between the cellulose molecules themselves which constitute the yarn, a result quite opposite to that resulting from the normal saponification.

i As an example of a method of carrying out our invention, we give the following:

Example Skeins of cellulose acetate were extracted to remove lubricants, dried at'100 C. and

weighed. These skeins were then conditioned in normal atmosphere and then suspended in a large aspirator connected with a-flask containing an aqueous'solution of ammonia of 28% strength. The aspirator was sealed and a very thin layer of ammonia solution maintained on its base. About every hour during the first eight hours of reaction, the skeins were shaken out and turned. The temperature in the aspirator was maintained at 27 to 29 C. The yarn employed was 150 denier and contained 26 filaments and had an approximate acetyl value of 54.5%.

At the end of 2 hours, cellulose acetate treated as above was found to besaponified 1.4% at the end of 5 hours, 6.10% at the end i of 7 hours, 30.8% at the end of 8 hours, 56%

at the end of 10 hours, 95%; at the end of 24 hours, 99.2%. Even when saponified as much as 56%, the material was resistant to cotton dyes. Cellulose ester materials saponified in accordance with this invention were found to possess a pronounced resistance to delustering on boiling when the percentage of saponification exceeded 90%. a I

Another distinctive property of the saponified material is the percentage regain of moisture. This is a very valuable property for not only does it offset the loss in weight due to saponification but it also renders the material more pliable. This is particularly valuable for yarns of cellulose ester material since it renders them more suitable for use in the various textile operations. This is true of both organic and inorganic esters of cellulose.

The following table shows the percentage regain of moisture of cellulose acetate after claim and saponification.

Hours Per cent Per cent 581mm sap'onifieation regain fled Blanknone 3 1 0.11 a s1 2 1.4 4.03 a 2.0 tea 4 s02 4.81 5 e1 4140 6 12. 45 6. 41 1 30.8 7.98 8 56. 01 8. 6O 10 7a 10 9.19 12 85.00 9.38

The resistance to heat of cellulose ester material saponified by thisprocess is also increased. The amount of increase of heat resistance varies with the degree of saponification, the lower the degree of saponification the higher the temperature at which the material can be ironed or otherwise treated without being scorched or otherwise affected in its appearanc Examples of cellulose esters which may be treated in accordance with this invention are cellulose r'ormate, cellulose propionate, cellulose butyrate, etc. While the specific description has dealt largely with cellulose acetate, the invention is not to be considered as limited thereto but as applicable to all cellulose esters and the term cellulose esters as used in the claims is to be so interpreted. The term, of saponification as used in the description and claims is calculated on the loss in dry weight and is quoted as of acetyl groups lost, assuming an original acetyl value of 54.5%.

Having described our invention what we desire to secure by Letters Patent 1. Process of saponifying cellulose esters which comprises subjecting materials containing the same to the action of a saponifying'agent in vapor form under such condito at least partially saponify the cellulose esters and in the presence of moisture.

2. Process of 'saponifying materials containing cellulose esters which comprises treating the. same with a vaporous 'saponifye ing agent in the presence of moisture.

3. Process of saponifying materials containing cellulose esters which comprises subj'ecting the same to the action of an atmosphere containing vapor of a base. and moisture.

4. Process of saponifying 'materials containing organic esters of cellulose which com-' prises treating the same with a: vaporous saponifying agent in the presence of moisture. l

5. Process of saponifying materials containing cellulose acetate which comprises treating the same with a va orous saponifying agent in the presence 0 moisture.

6. Process of saponifying materials containing organic esters of cellulose which comprises subjecting the s'ame to the action of an atmosphere containing ammonia and water vapor, the amount of ammonia present being suflicient at least partially to saponify the organic esters of cellulose.

7 Process of saponifying materials conresulting from the vaporization of a 28% aqueous solution of ammonia.

10. Process of increasing strength of cellulose ester materials which comprises saponifying the cellulose estermaterial with a saponifying agent in vapor form undersuch, conditions as to at least partially saponify the cellulose esters and in the presence of moisture.

. 11. Process of increasing the tensile strength of organic ester of cellulose materials which comprises saponifying the organic ester of cellulose material with a saponifying agent in vapor form inthe presence of moisture.

12. Process of increasing the tensile strength of cellulose acetate materials which comprises s'aponifying the cellulose acetate material with a saponifying agent in vapor form in the presence of moisture.

13. Process of increasing the tensile strength of cellulose acetate materials which comprises saponifying the cellulose acetate material in an atmosphere containing ammonla and moisture in vapor form. I

14. Method of treating textile materials contam ng filaments of organic esters of cellulose comprising at least partially saponifythe tensile ing the organic ester of cellulose with a saponifying agent in vapor form in the presence of inoisture.

15. Method of treating textile materials containing filaments of cellulose acetate comprising at least partially saponifying the cellulose acetate with a saponifying agent in vapor form in the-presence of moisture.

. In testimony whereof, we have hereunto subscribed our names. 7 CAMILLE DREYFUS.

WILLIAM WHITEHEAD. 

